1. Technical Field
The present invention relates to an imaging device which focuses a subject by a phase difference AF method, a focusing method thereof, and a non-transitory computer readable medium storing a focusing control program.
2. Related Art
An auto focus (AF) system, which is mounted in an imaging device such as a digital still camera, mainly includes two systems, which are a phase difference AF system and a contrast AF system. Between the two systems, the phase difference AF system has an advantage of having a high focusing speed, so as to be generally employed to a single lens reflex camera.
However, when a distance to a major subject is measured by the phase AF system several times and a focusing operation of a focus lens is performed using the measurement results after several attempts, the measurement results may not be consistent. Further, when camera panning is performed, a distance to a major subject is suddenly changed. Also in this case, when the focusing operation of the focus lens is performed based on the measurement result of the phase difference AF system, movement of the focus lens is too quick, so that the focusing operation is inappropriate and a defocused image may be captured.
Therefore, in the related art disclosed in Patent Literature 1 (JP-A-H08-146286), the focusing operation is performed using an average of a predetermined number of measurement results. When the measurement result is inconsistently changed, the focusing operation is performed excluding the inconsistent measurement results.
In the related art disclosed in Patent Literature 2 (JP-A-H05-27157), four measurement results immediately before photographing are averaged to be used for the focusing operation and when the measurement results are continuously and significantly changed, an auto-focus operation does not performed.
In the related art disclosed in Patent Literature 3 (JP-A-H02-15225), when the measurement result is significantly changed, it is determined that the change is caused by camera panning, so that the auto-focus operation cannot be enabled.